1. Field of the Invention
The present invention relates to a magnetoresistance effect element, and a magnetoresistance effect sensor and magnetic information detecting system using same, and more particularly, to a magnetoresistance effect element for reading magnetic information recorded on a magnetic recording medium, and a magnetoresistance effect sensor and magnetic information detecting system using same.
2. Description of the Related Art
In the prior art, magnetic reading converters called magnetic resistance (MR) sensors or MR heads are known. These read data from the surface of a magnetic recording medium at a large linear density. MR sensors and the like detect a magnetic field by detecting changes in resistance produced by reading elements in accordance with the surrounding magnetic field, and converting these changes to a magnetic field signal. In this, a magnetic signal detected by a reading element is detected as a function of the strength and direction of the magnetic flux. In a conventional MR sensor of this kind, one component of the resistance of the reading element changes in proportion to the square of the cosine (cos.sup.2) of the angle between the direction of magnetization and direction in which the sensor current flows through the element. This is called the `anisotropic magnetic resistance` (AMR) effect.
This AMR effect is commonly known and therefore is not described here, but a detailed explanation thereof can be found, for example, in "Memory, Storage and Related Applications," IEEE Trans. on Mag. MAG-11, p.1039 (1975), by D. A. Thompson, et. al. In magnetic heads using the AMR effect, often a longitudinal bias is applied in order to suppress Barkhausen noise, and in some cases, an anti-ferromagnetic material, such as FeMn, NiMn, nickel oxide, or the like, is used as a material for supplying this longitudinal bias.
Furthermore, recently, in resistance change in laminated magnetic sensors, remarkable magnetoresistance effects have been discovered due to spin-dependent transmissivity of conducting electrons between magnetic layers which are placed to either side of a non-magnetic layer, and spin-dependent scattering at the accompanying layer interfaces. This magnetoresistance effect is known by various names, including "massive magnetoresistance effect" or "spin valve effect", or the like. Magnetic resistance sensors of this type are made from suitable materials, and they have improved sensitivity and display a greater resistance change with respect to a magnetic field compared to sensors using the AMR effect. In MR sensors of this kind, the internal resistance in the plane between the ferromagnetic layers separated by a non-magnetic layer is proportional to the cosine of the angle between the directions of magnetization of the two layers.
Japanese Unexamined Patent 2-61572 which has a claim of priority based on an application dated Jun. 16, 1988 discloses a laminated magnetic structure which produces a high MR effect caused by non-parallel arrangement of the magnetization of the magnetic layers. In the aforementioned patent, ferromagnetic transition metals and alloys are cited as materials which can be used in this laminated magnetic structure. Furthermore, the patent also discloses that it is suitable to add an anti-ferromagnetic layer as one of the at least two magnetic layers separated by an intermediate layer, and FeMn is appropriate for this anti-ferromagnetic layer.
A further MR sensor is disclosed in Japanese Unexamined is Patent 4-358310 which has a claim of priority based on an application dated Dec. 11, 1990. This MR sensor comprises two thin film layers of ferromagnetic material divided by a thin film layer of non-magnetic metallic material. When the applied magnetic field is zero, the directions of magnetization of the two ferromagnetic thin film layers are orthogonal, and the resistance between the two unconnected ferromagnetic layers changes in direct proportion to the cosine of the angle between the directions of magnetization of the two layers, thereby producing an MR sensor which is not dependent on the direction of the electric current flowing through the MR sensor.
Japanese Unexamined Patent 6-203340 which has a claim of priority based on an application dated Nov. 17, 1992 discloses an MR sensor which incorporates two thin film layers of ferromagnetic material separated by-a thin film layer of non-magnetic metallic material. This MR sensor is based on the effect that when the applied external magnetic field is zero, the magnetization of the adjacent anti-ferromagnetic layer remains orthogonal with respect to the other ferromagnetic layer.
Furthermore, Japanese Unexamined Patent 7-262529 (application dated Mar. 24, 1994) discloses a magnetoresistance effect element which is a spin valve comprising a first magnetic layer/non-magnetic layer/second magnetic layer/anti-ferromagnetic, and more particularly one which uses CoZrNb, CoZrMo, FeSiAl, FeSi, or NiFe, or a material wherein Cr, Mn, Pt, Ni, Cu, Ag, Al, Ti, Fe, Co, or Zn is added to these, in the first and second magnetic layers.
Furthermore, Japanese Unexamined Patent 7-202292 (application dated Dec. 27, 1993) discloses a magnetoresistance effect film characterized in that, in a magnetoresistance effect film comprising a plurality of magnetic thin films laminated between non-magnetic layers on a substrate, wherein an anti-ferromagnetic thin film is provided in one of the soft magnetic thin layers which are mutually adjacent via the non-magnetic thin layer, and Hc2&lt;Hr, taking the bias magnetic field of this anti-ferromagnetic thin film as Hr and the coercive force of the other ferromagnetic thin film as Hc2, the aforementioned anti-ferromagnetic material is at least one of NiO, CoO, FeO, Fe.sub.2 O.sub.3, MnO, or Cr, or a mixture of these.
Furthermore, Japanese Patent Application 6-21487 (application dated Sep. 8, 1994) and Japanese Patent Application 6-269524 (application dated Nov. 2, 1994) propose a magnetoresistance effect film characterized in that, in the aforementioned magnetoresistance effect film, the anti-ferromagnetic material is a superlattice comprising at least two of NiO, NiXCol--XO and CoO. Japanese Patent Application 7-11354 (application dated Jan. 27, 1995) proposes a magnetoresistance effect film characterized in that, in the aforementioned magnetoresistance effect film, the anti-ferromagnetic material is a superlattice comprising at least two of NiO, NiXCol--XO (x=0.1-0.9) and CoO, and the atomic ratio of Ni with respect to Co in this superlattice is equal to or greater than 1.0. Japanese Patent Application 7-136670 (application dated Jun. 2, 1995) proposes a magnetoresistance effect film characterized in that, in the aforementioned magnetoresistance effect film, the anti-ferromagnetic material has a two-layer structure comprising CoO laminated to a thickness of 10-40 Angstrom on NiO. However, the magnetoresistance effect films using oxides in the anti-ferromagnetic layer, as disclosed in the aforementioned patent publications and applications, are subject to great stress in the oxide anti-ferromagnetic layer, and therefore a problem arises in that the anti-ferromagnetic layer peels away from the base layer due to local current heating effects when the sensor current passes through the element, thereby causing the element to break down.